I know I need to rotate my plants for next year , I made the mistake of planting potatoes in the same place two years running , and that mistake is showing now. ( I don't have good soil to begin with , I'm working on that)

But I just don't want to randomly rotate the plants, I want to place them where they can do the soil the most good.

I know enough for example not to put the tomatoes where the potatoes were, but I don't know if putting the onions were the tomatoes were is bad, or putting sqash where the onions were is a good idea and so forth.

Every plant takes certain nutrients from the soil ( some add ) if keep planting the same plants in the same area some key nutrient will depleted from the soil.

Secondly, the various pest we all hate that have the nerve to eat our veggies will overwinter in the ground near the plants they like best, by rotating crops, when they emerge in the spring, they won't have a food supply (hopefully) and will die out, or at least be controlled.

I should have mentioned, the plants I have in that diagram are only my "main" plants, I always have some sort of "filler" plant between rows

This year I had two rows of potatoes with a row of peas in between, between the onions and and leeks I had carrots, and with the squash I had some radish , I harvested all the radish except for two so I could harvest the seeds, and they can act as a "trap crop"